Is This Woman Spinning Left or Right?

I've been staring at Nobuyuki Kayahara's "spinning dancer" for five minutes straight, and I feel like I'm being hypnotized. To me, this silhouetted woman looks like she's rotating counterclockwise, but every so often, for a fleeting moment, she reverses her spin.

It's maddening, because I know this is all in my head. The spinning dancer is on an infinite loop. She never changes. Yet some people see her spinning clockwise, and some see counterclockwise. A video on Youtube explains that this has to do with which side of your brain is more dominant. If your right hemisphere dominates, you see her spin clockwise; if your left brain dominates, then you see her move counterclockwise. And apparently, people with high IQs can see the girl spinning in both directions. Does that mean I'm a genius because I see her spin both ways, or an idiot because I can't control it?

I want to know what's going on in my brain, so I call up Arthur Shapiro and Niko Troje, a pair of scientists who dissect Kayahara's spinning girl in the forthcoming Oxford Compendium of Visual Illusions. I run the Youtube theory by them. "That's just gibberish," says Shapiro, a computer science professor at American University and creator of the color wagon wheel illusion. The reason we see her spinning in different directions is actually much more complex than which side of our brain dominates.

I'm feeling good now, because I'm realizing that you don't have to be freaking Neil deGrasse Tyson to enjoy this thing. I tell Shapiro and Troje how frustrating it is to feel powerless over my brain, and I ask if they can help me spin the spinning lady in both directions. They're game.

But before they do, they say that it's important to understand that the spinning girl falls under a class of optical illusions called reversible images. Even though she spins, she bears similarities to other static illusions, like Necker cubes.

The Necker cube can be seen in two ways: either the lower right panel is in the front, or it's in the back. Reversible images like this flip on us because they're ambiguous, says Troje, director for BioMotion Lab at Queens University. They don't provide enough depth clues to make definitive sense. Your brain doesn't like when images don't make sense, so it imposes meaning where there isn't any. It's guessing. We do this all the time, says Shapiro. "Because in a general sense, the world is full of low-information environments." Take driving at night. You brain projects pavement into the darkness, because if it didn't, you'd be too terrified to drive. With the spinning girl, there's a lot of darkness, especially around the clues that help shape perspective. "Silhouettes are supremely ambiguous," says Shapiro. "If you added data to the spinning girl, like a pair of colorful Lululemon pants, your brain would solve the illusion faster."

Indeed, by simply adding contour lines like in the below two videos, spinning girl ceases to mystify. She appears to spin in one direction only.

But that feels like cheating, and Shapiro assures me that I can solve the illusion with my own brain. "Cover up everything but her foot touching the ground," he says. Relax. Watch the foot. Look at the shadow beneath her. Now imagine you are physically moving up or down in space. "If you want her to switch directions, look at her as if you're filming her from below. Now pretend to be filming her from above." Indeed, the spinning girl moves counterclockwise if I imagine myself below her, and clockwise if I imagine myself above her.

Shapiro and Troje tell me that most people initially see the girl spinning clockwise. But since I tend to see her spinning counter-clockwise, I'm imagining her above me. Does that make me dumber than the average person? No, they assure me. (Did I mention that I like these guys?) Nor do my counter-clockwise tendencies provide any clues as to whether I'm right- or left-brained. "We know there are different tasks done in different hemispheres, but saying someone is more dominant one way, well, that's tricky," Shapiro says.

Shapiro and Troje explain that seeing the girl spin one way or another likely isn't about hemispheres at all.As proof, they point me to the vast body of "split brain research," and, whoah, is it weird and gross and fascinating.

Beginning in the 1960s, scientists were trying to provide relief to epileptic patients. They thought they could prevent the spread of seizures from one hemisphere to the other if they severed the connection between the right and left brain. So that's what they did: They cut the patients' corpus callosum, the connecting fibers running between the two hemispheres.

The scientists assumed that these split-brain patients would be unable to verbally name objects presented to their left visual field, because things in the left visual field hook up to the right side of the brain, which is where we process nonverbal thinking. Some patients were indeed unable to identify the objects, but others could. And the scientists were baffled. So they tried little games, like placing a dot in the patient's left visual field, followed by a dot in their right visual field. Rather than see the dot disappear and reappear, the epileptics saw it as being in continuous motion, moving from left to right, despite their split hemispheres. Their brains were filling in missing data with the most likely scenario, and scientists concluded that we have not one but two separate visual systems: the recently evolved corpus callosum, which links up color- and language-identifying regions of the brain, and an older subcortical system that's sensitive to movement and orientation (and presumably kicked into action when the corpus callosum was severed).

The fact that a majority of people see the girl spinning clockwise, then, likely has more to do with our hyper-vigilant subcortical system, which runs in the background, free from the tyranny of brain hemispheres. Here's the logic: Things, including those that could hurt us, are more likely to sit on the ground, Troje says. It's to our advantage to quickly recognize a snake stretched across a dark path, for instance. So when presented with ambiguous visual information, people tend to register the images as though they're looking downward. Take another glance at the Necker cube. Odds are you see that one from an above-down angle, too.

It's a lot to process. One the on hand, the researchers are telling me that I'm not dumb. That's good. But on the other, they seem to be implying that I'm more likely than the average person to be bitten by a snake. Right? Or no? Maybe I've just been staring at a screen for too long.